Assessing the contact-mediated role of netrin1 in axon guidance

评估 netrin1 在轴突引导中的接触介导作用

• 批准号: 9815911
• 负责人: SAMANTHA J BUTLER
• 金额: $ 44.44万
• 依托单位: UNIVERSITY OF CALIFORNIA LOS ANGELES
• 依托单位国家: 美国
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-07-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9815911
• 关键词: Adhesions; Adhesives; Axon; Biological Assay; Cells; Chemotaxis; Chickens; Collection; Complex; Cues; Data; Deposition; Development; Diffuse; Disease; Embryo; Environment; Event; Family; Floor; Ganglia; Genetic; Geometry; Goals; Growth; Growth Cones; Hedera; Image; In Vitro; Injury; Laminin; Lateral; Maps; Mediating; Membrane; Modeling; Molecular; Mus; Muscle fasciculation; Mutation; Natural regeneration; Nervous system structure; Neurodevelopmental Disorder; Neurons; Phenotype; Plant Roots; Play; Positioning Attribute; Process; Prosencephalon; Radial; Resolution; Role; Signal Transduction; Source; Spinal; Spinal Cord; Surface; Synapses; Telencephalon; Textbooks; Tissues; Ventricular; axon growth; axon guidance; axonal guidance; brain malformation; cell growth; cell type; corticofugal fiber; diencephalon; domain mapping; genetic approach; member; nerve stem cell; neural circuit; receptor; regenerative; repaired; uptake

The establishment of neural circuits requires neurons to extend axons over considerable distances, using molecular cues in the embryonic environment to orient their growth cones. The textbook example of a guidance factor is netrin1, a member of the laminin superfamily first characterized in the spinal cord. Classic studies suggested that netrin1, produced by floor plate (FP) cells, acts by chemotaxis, diffusing over long distances to guide Dcc+ commissural axons towards the FP. Netrin1 was then implicated in guidance decisions throughout the nervous system. However, our studies have recently demonstrated that the key source of netrin1 is neural progenitor cells (NPCs) in the spinal ventricular zone. Rather than acting as a long-range diffusible gradient, our data supports a model in which NPC-derived netrin1 acts locally, forming a directional path for axons that also promotes axonal fasciculation. The bipolar geometry of NPCs permits them to deposit netrin1 at the basal (pial) margins of the spinal cord. This netrin1+ substrate then acts locally to direct fasciculated, ventral axon extension by haptotaxis, the directed growth of cells along an adhesive surface. However, netrin1 may mediate a more complex activity for axons beyond pure adhesion: netrin1 is then deposited onto Dcc+ axons, and these axons then grow precisely around the border of VZ, i.e. a netrin1- expressing domain. Ablating a small region of netrin1 expression causes axons deviate from their trajectory to follow the ectopic netrin1 boundary. We propose to call this collection of activities a “hederal” growth boundary, from the analogy of a wall supporting the growth of ivy (genus: hedera) that is not itself penetrated by the ivy. Netrin1 can form a local growth substrate, and promote the fasciculated growth of axons around a netrin1-expressing domain. This reinterpretation of the mechanistic basis by which netrin1 functions, explains why little progress has been made using soluble netrin1 as a regenerative factor. To further this goal, we will assess [1] the mechanisms by which spinal NPCs establish a netrin1+ haptotactic substrate that promotes directed, fasciculated axonal growth in Aim 1, [2] whether NPC vs FP cells have distinct roles producing netrins in Aim 2 and [3] whether netrins have haptotactic activities in axon guidance in the forebrain in Aim 3. Aim 1: Determine the mechanism by which spinal NPCs establish netrin1 “hederal” boundaries Hypothesis: Spinal NPCs traffic netrin1 to the pial surface to establish a haptotactic substrate. Netrin1 then transfers to Dcc+ axons to promote their fasciculated axon growth around netrin1-expressing regions. Aim 2: Determine the range role of FP-derived netrin1 in the spinal cord Hypothesis: FP-derived netrin1 acts over short range to fasciculate commissural axons crossing the midline Aim 3: Determine the role of NPC-derived netrin1/3 in the forebrain Hypothesis: Neural progenitors in the developing forebrain use the netrin family to establish growth boundaries that guide axons between the diencephalon and telencephalon.

神经回路的建立需要神经元将轴突延伸相当长的距离 距离，利用胚胎环境中的分子线索来定向它们的生长锥。教科书 指导因子的例子是 netrin1，它是层粘连蛋白超家族的成员，首先在脊髓 绳索。经典研究表明，netrin1 由底板 (FP) 细胞产生，通过趋化作用、扩散作用发挥作用。 长距离引导 Dcc+ 连合轴突朝向 FP。 Netrin1 随后被牵涉到 整个神经系统的指导决策。然而，我们最近的研究表明， netrin1 的主要来源是脊髓心室区的神经祖细胞 (NPC)。而不是充当一个 长程扩散梯度，我们的数据支持一个模型，其中 NPC 衍生的 netrin1 局部作用，形成 轴突的定向路径也促进轴突束颤。 NPC 的双极几何结构允许它们 将 netrin1 沉积在脊髓的基底（软脑膜）边缘。然后，该 netrin1+ 底物局部作用 通过趋触性直接束状、腹侧轴突延伸，细胞沿着粘合剂定向生长 表面。然而，netrin1 可能介导轴突超越纯粹粘附的更复杂的活动：netrin1 是 然后沉积到 Dcc+ 轴突上，然后这些轴突精确地围绕 VZ 边界生长，即 netrin1- 表达域。消除 netrin1 表达的一小部分区域会导致轴突偏离其轨迹 遵循异位 netrin1 边界。我们建议将这一系列活动称为“hederal”增长 边界，来自支持常春藤（属：常春藤）生长的墙壁的类比，但其本身并未被穿透 常春藤旁。 Netrin1可以形成局部生长基质，促进轴突周围的束状生长。 netrin1 表达域。这种对 netrin1 功能机制基础的重新解释解释了 为什么使用可溶性 Netrin1 作为再生因子几乎没有取得进展。为了进一步实现这一目标，我们将 评估 [1] 脊髓 NPC 建立 netrin1+ 趋触底物的机制，该底物促进 目标 1 中的定向、束状轴突生长，[2] NPC 与 FP 细胞是否具有产生 netrins 的不同作用 在目标 2 和 [3] 中，netrins 是否在目标 3 的前脑轴突引导中具有趋触活性。 目标 1：确定脊髓 NPC 建立 netrin1“hederal”边界的机制 假设：脊髓 NPC 将 netrin1 运输到软脑膜表面以建立趋触基质。那么 Netrin1 转移到 Dcc+ 轴突以促进其在 netrin1 表达区域周围的束状轴突生长。 目标 2：确定 FP 衍生的 netrin1 在脊髓中的作用范围 假设：FP 衍生的 netrin1 在短距离内作用，使穿过中线的连合轴突束成束 目标 3：确定 NPC 衍生的 netrin1/3 在前脑中的作用 假设：发育中的前脑中的神经祖细胞使用 netrin 家族来建立生长边界 引导间脑和端脑之间的轴突。